This spring I sat in an auditorium in New York and watched two heroes of that international movement, Kris Kobach and Tom Tancredo, list their reasons why immigration has pushed the United States to the breaking point: Immigrants want to take space but there is no space left. Immigrants want to take jobs but there are no jobs left. Immigrants want to take welfare checks -- our "goodies", said Kobach with a smile -- but there is no money left. It would be nice if America could still be the land of opportunity, they say, as it was for their own ancestors. But America was strong then. It's weak now, so weak that more immigrants will push it right over the edge.

These immigration opponents are planning a funeral for America. But I won't attend; America is not dying. When I walked out of that auditorium and looked around, I didn't see the broken, limping, moribund country I had just been told about. This country, my country, has proven the pessimists wrong again and again. Its proud history deserves more optimism and faith than this.

Folks who find that there's no room left in America should take a drive across Kansas, Mr. Kobach's base of operations. Here's what that drive looks like. It doesn't look that different from how Ohio looked when my immigrant ancestors settled there in the 1840s -- still wide open, though with better infrastructure.

We can also politely ignore the anti-immigration groups who rest their arguments on high unemployment rates. The same groups were saying exactly the same things four years ago, when the economy was at full employment. Wherever their interests lie, it's not in economic analysis of labor markets. On employment and immigration, the history of this great and dynamic nation is clear: In 1905, the unemployment rate was about 5%. A century later, the U.S. population had quadrupled, and the unemployment rate was about 5%. The tens of millions of immigrants and their children turned out to be not just workers, but also consumers, and consumption puts others to work. Meanwhile the average American got several times richer, in real terms. Americans, many of them immigrants, created types of employment and invented entire industries that could not have been dreamed of in 1905. As for today's crisis: America has been through much worse -- years of 30% unemployment, in my grandma's generation -- and gone on to prove the pessimists wrong then, too.

And what about those "goodies" that immigrants supposedly come to take, the goodies that immigration opponents' sickly, dying version of America can no longer afford to give? Here again, immigration opponents' worst nightmare has already happened. As the US population quadrupled over the past century, America built and has maintained a safety net for its poorest citizens. If I retire without savings, if I'm laid off from my job, if I'm too poor to buy health care, food, or housing, the government can and will help. Yes immigration can strain local governments' coffers even as it fills national coffers, but this can be addressed by fiscal systems designed around the reality of immigration. Still, many immigration opponents will tell you that the next few immigrants will take so many goodies that the whole system risks collapse. Strange thing is, they were saying that 20 years ago, and 20 years before that, and 20 years before that.

For immigration opponents, America's demise seems always just around the corner. I wish them well in their long wait for America to come crashing down. My own feeling is that America's best years are still to come. The fact that some people are willing to sit on 23 year-long waiting lists for the chance to live in the United States suggests that I'm not the only optimist about this country's future.

The economics are clear: every serious economic study indicates that more international migration will create more and better jobs, and greatly strengthen the flagging world economy. Beyond that, international migration is a massively powerful force for development: International migration has caused about half of the poverty reduction that has occurred for people born in Mexico, and most of the poverty reduction that has occurred for people born in Haiti. Next year migrants will remit about $375 billion to developing countries, multiple times the value of all foreign aid put together. Migrants and migration are a powerhouse for global development.

The economic evidence is not on the pessimists' side. International Migrants Day deserves celebration, as does the strength and the greatness of the places migrants go.